1. Field of the Invention
This invention relates generally to photographic cameras and, more particularly, to automatic, powered film winding mechanisms in cameras.
1. Description of the Related Art
Many photographic cameras include self-powered film winding mechanisms that automatically move a strip of photographic film within the camera before each exposure is produced. Typically, a small electric motor powers a gear train that is coupled to a film spool. One end of the film strip is attached to the spool so that operating the motor causes the gear train to rotate the spool, which moves the film. The motor is operated for a sufficient time before each exposure to ensure that a fresh, unexposed frame of film is at an exposure gate and any previously exposed frame is moved away. Typically, the motor is coupled to a shutter mechanism so that moving the film also cocks a shutter for making an exposure. Such automatic film winding, also referred to as an "autowind" feature, makes the camera easier to use and has become quite popular.
Another popular consumer item is the single-use camera, comprising an inexpensive housing that contains a length of photographic film and picture-taking components such as a viewfinder, an objective lens, a shutter mechanism, and a film transport mechanism. After a consumer purchases the film-containing single-use camera and exposes the entire length of film, the consumer provides the camera to a film processor for film development and printing. The film processor extracts the film, develops it, and provides the consumer with the processed film and prints. In this way, the single-use camera is very convenient. The consumer does not re-use the camera, hence the term single-use camera. Instead, the film processor returns the housing and camera components to the manufacturer for refurbishing. The refurbished camera, with a new load of photographic film, is then sold once again to a consumer. A design goal for a single-use camera with an autowind feature is to incorporate all film drive components within the camera housing at minimal expense. Therefore, the motor used to move the photographic film is relatively small and inexpensive. A gear train with a high reduction ratio is typically required because the motor output shaft is small and such a motor usually produces relatively low torque output. The high gear reduction ratio also is required so that the motor torque can be carefully and precisely applied. Torque must be very carefully applied in the film exposure direction because the film must be moved very precisely to maintain frame-to-frame spacing. Application of torque is not so critical in the film rewind direction.
Although the gear reduction must be achieved in a limited amount of space, the high gear reduction ratio can require a relatively large number of gear components. The gear reduction often is achieved through a gear train that includes seven or more spur gears.
In U.S. Pat. No. 4,322,149 to Maida et al., for example, a motor powers a gear mechanism comprising up to ten gears for forward film movement. The Maida system includes a motor that drives an axially slidable gear. The gear meshes with one gear to move film forward in a wind-up direction and meshes with a different gear to rewind the film. In the forward film direction, the motor drives a series of spur gears that in turn drives a planetary gear arrangement that rotates a film coupling. The film coupling can be connected, for example, to a film take-up spool.
In a single-use camera, film is moved only in one direction. Typically, the film is wound back into the cartridge as exposures are made. A consumer who purchases a single-use camera, therefore, does not have to rewind the film for removal from the camera, as this action is performed by a photofinisher. As noted above, however, the application of torque that must be most precisely controlled and that particularly requires high gear reduction is in moving the film in the exposure direction. Thus, single-use cameras with an autowind system typically have reduction gear trains with many components, such as described above.
In a conventional autowind system for a single-use camera, the large number of gears necessary to achieve the required gear reduction ratio adds to the cost of the autowind system and increases the amount of space necessary to contain the gear mechanism. Any increase in the size of the single-use camera housing necessary to contain the autowind gear mechanism adds to the cost and reduces the user convenience of the camera. The large number of spur gears in the autowind mechanism also makes camera assembly more difficult.
From the discussion above, it should be apparent that there is a need for a photographic camera with an automatic film winding mechanism that can be provided with a minimal number of components in a small space and that can be produced at reduced cost. The present invention fulfills this need.